[Xen-devel] Re: Need help with fixing the Xen waitqueue feature

To:	Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
Subject:	[Xen-devel] Re: Need help with fixing the Xen waitqueue feature
From:	Olaf Hering <olaf@xxxxxxxxx>
Date:	Wed, 9 Nov 2011 08:02:17 +0100
Cc:	xen-devel@xxxxxxxxxxxxxxxxxxx
Delivery-date:	Tue, 08 Nov 2011 23:03:29 -0800
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On Tue, Nov 08, Andres Lagar-Cavilla wrote:

> Olaf,
> are waitqueue's on the mem-event ring meant to be the way to deal with
> ring exhaustion? i.e. is this meant to go beyond a testing vehicle for
> waitqueue's?

Putting the guest to sleep when the ring is full is at least required
for p2m_mem_paging_drop_page(), so that the page gets informed about all
gfns from decrease_reservation.

> With the pager itself generating events, and foreign mappings generating
> events, you'll end up putting dom0 vcpu's in a waitqueue. This will
> basically deadlock the host.

Those vcpus can not go to sleep and my change handles that case.

Olaf

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[Xen-devel] Re: Need help with fixing the Xen waitqueue feature